Pancreatic cancer is an exceptionally aggressive cancer. It is the fourth leading cause of cancer death in the United States and is increasing in incidence. One of the major factors contributing to the high fatality of pancreatic cancer is the poor responses of most pancreatic cancer patients to radio- and chemo-therapy. Our long-term goal is to understand the molecular mechanisms underlying the exceptional radio- and chemo-resistance in pancreatic cancer. We have recently succeeded in creating pancreatic cancer isogenic cell lines that differ in radiosensitivity from the parental cells. The radioresistant cel lines were generated by exposing pancreatic cancer cells to fractionated ionizing radiation programmed in a way that mimics a typical course of radiotherapy. We hypothesize that the acquired radioresistance in the pancreatic cancer cells are conferred by the aberrant expression of one or more proteins that are involved in cell proliferation and/or survival. Our preliminary results show that several pathways in the radioresistant pancreatic cancer cells have been markedly altered. We propose to use advanced subcellular fractionations, novel quantitative proteomic profiling, and bioinformatics analysis to systematically identify the proteins that are mostly likely to be responsible for the acquired radioresistance in the pancreatic cancer cells (Specific Aim 1), and use molecular and cell biology methods to functionally characterize a well-defined set of the identified proteins with regards to their roles in radio- and chemoradio-resistance in pancreatic cancer (Specific Aim 2). The results from the proposed work will contribute to understanding the molecular mechanisms underlying the exceptional radio- and chemoradio-resistance in pancreatic cancer, and will contribute to designing new strategies to improve the cure rate of pancreatic cancer.